AUQ engine horrible stutter and misfire code

[Nautilus]

Hello everyone

Had the unpleasant experience of a CEL and stutter last night, when under boost. Went to a shop this morning, checked with VAG-COM, found out the even more unpleasant list of symptoms:

Code: 16684 - Random/Multiple Cylinder Misfire Detected
no other codes for each cylinder

Horrible stutter under boost

CEL blinking under boost
CEL on all the time otherwise

Very hard to raise boost over 0.5 bar, but it does not fluctuate the slightest bit

Loss of power

High idle, sometimes over 1000rpm

Increased fuel consumption

Pulled the sparkplugs (NGK BKR7E, 31k kms on them) and checked, color of dark wet sand, no deposits, correct .028" gap

Changed 2 of the coils (had burn marks inside, where the sparkplug touches) with 2 older coils from my toolbox, no difference

Tried to run with MAF disconnected, no difference

Throttle body had just been cleaned and polished inside

Air filter is brand new

Slight stutter on idle, no stutter if no boost is present, harsh stutter under boost, tries to rip the steering wheel at 1 bar

Sparkplugs booked to be changed on Monday.

Which else may be?

Thank you,

~Nautilus

 

[big rich]

9 times out of 10 its s coil pack for those symptoms

 

[Nautilus]

All 4 of them at once? Even as I've changed 2 coils and still no improvement?

~Nautilus

 

[Mr OCD]

All 4 of them at once? Even as I've changed 2 coils and still no improvement?

~Nautilus

You need to log ignition misfires using vagcom ... this will tell you which coilpack is faulty... I had two go at once on mine. Replaced all four anyway.

 

[big rich]

No not all four at once but you might aswell replace all four with new to avoid future failiures.

 

[Nautilus]

OK, thanks. 4 coils and 4 sparkplugs.

I expected a coil failure (the last set died at 44k kms, now 42k kms more had passed, so they were just in the timeframe), but there was no specific code for one cylinder and replacement of 2 coils didn't make the slightest difference.

So either all 4 coils are about to die, or there is something more: harness, boost leak, fried sensor, dead MAF. Out of which the coil wire harness is the hardest to find and to fit.

Which brand of coils holds best under the heat of a 1.8T engine bay?

~Nautilus

 

[big rich]

Only go for genuine ones. If you have spares which you know are ok, swap them one by one till you find which one is defective. Then you can rule out anything else causing it.

 

[Nautilus]

This month I need money as much as I need air, but if a set of 4 new coils solves the issue, I would gladly change them all for the peace of mind.

~Nautilus

 

[Nautilus]

Bolt-down coils (code 06B 905 115E, from Hitachi or other manufacturer) are more solid than classic 1.8T coils, or it's just a myth and they will just as well die in 40k kms?

~Nautilus

 

[Nautilus]

Changed the coils for a Beru set, changed the sparkplugs to a set of NGK BKR7E-SC11 gapped to 0.8mm / 0.032". Deleted the codes in VAG-COM. CEL did not come on. Acceleration smooth throughout the rev range, no more stuttering.

However idle was very lumpy and irregular.

As I've cleaned the throttle body Saturday, aligned it by leaving the ignition on until it does not buzz anymore, then started. Drove for about 50 miles, city and highway. Very hard to raise boost above 0.5bar, but ran and accelerated fine.

After the drive, idle lowered itself slowly when the pedal was released, then it stood slightly above 1000rpm (normal idle is 720rpm).

Engine smooth running otherwise. No more idle lumpiness, but idle still high.

Does it have anything to do with throttle body cleaning? And if so, will the ECU adapt itself in time?

Can the throttle body be lubricated with something?

Cleaning went like this: unscrewed the throttle body, separated the intercooler hose, left small hose and wires attached, cleaned with rag and brake cleaner, rubbed the stubborn dirt with a small wood splinter, wiped with rag and brake cleaner, moved the throttle plate to be sure it runs, re-assembled everything.

~Nautilus

 

[Mr OCD]

TB needs alignment with VCDS ...

 

[LEE69]

Why and how vag com is needed for a TB reset

 

[Nautilus]

Performed VAG-COM reset of the throttle body.

Dropped the idle rpm to 760-800 rpm.

Got an error code: Pressure Drop Between Turbo and Throttle Body - Check D.V.

Checked and tightened: intercooler to TB hose, TB itself on bolts, the three hoses of the DV. All of them tight.

Lumpy idle, rhythmic knock-knock-knock sound from the gearbox / airfilter side of the engine, where the EGR sits. Carbon canister does not make the usual ticking sound, but if the wire is disconnected it throws an "Oxygen Lambda Sensor" error code.

Engine runs smooth under boost.

After some time, idle goes back to normal, car runs as expected, good boost, up to 1.5bar. No codes.

After some driving, lumpy idle and weird sound from the are where the EGR is comes back, boost does not raise above 0.5bar (limp mode?)

After the next engine start, things appear normal. Then it can go back to lumpy idle and sound, randomly.

Is the EGR shot, and if so, why now? What does it have to do with TB and ignition?

~Nautilus

 

[Nautilus]

...Later edit: The EGR ("combi valve") may not be the culprit, as it should not drive the rpms up and down erratically as it happens, but the damn PCV valve (and its sister, the black pressure check valve on the intake, below the DV, a/k/a the "hockey puck valve") may be - for sometimes a faint smell of burnt oil creeps through the cabin air blowers.

The PCV valve below the manifold should be hard to change by myself?

~Nautilus

 

[Nautilus]

Tested also the PCV valve operation: engine on and idling, tried to open the oil cap, there is a sort of vacuum pulling on it, after removing the cap there is a "pulsation" of the air/gas in the block, making a thump-thump sound and blowing rhythmically through the oil cap hole.

PCV or hockey-puck valve?

~Nautilus

 

[Nautilus]

Removed the "hockey-puck" or "pancake" valve to check.

Spotlessly clean inside (due to my oil catch filter ), runs normally, air runs through all holes, diaphragm moves when sucking through it. Fitted back.

Checked the length of the breather hoses back to PCV below the manifold. No apparent holes or oily-air leaks.

Charcoal canister valve still does not tick when the engine is idling. It doesn't tick otherwise. It's dead.


~Nautilus

 

[Nautilus]

Let's judge strictly by the facts:

What went wrong: coils (old age, poor quality no-name, heat), sparkplugs (old age), throttle body (encrusted dirt).

What was tampered with: coils (replaced), sparkplugs (replaced), throttle body and its hoses (removed, cleaned and sealed back with a dab of silicone on the gasket to seal 100%), throttle body idling poorly (aligned in VAG-COM), carbon canister (does not tick).

So the boost / vacuum leak which causes lumpy idle should come from somewhere around the throttle body, where the hoses did not fit back properly.

It has 2 hoses: large IC to TB hose (triple checked, all clamps tightened by 7mm socket wrench to the max) and the small hose which comes from top of the TB and splits via check valves in 2 lines, one to the charcoal canister, one to a metal thin pipe over the manifold and.

Does a poor seal on the charcoal canister hose leak boost and vacuum?

After all, what does the canister do exactly? It filters something, but what?

~Nautilus

 

[Nautilus]

Got enraged by the idle issue, so I've traced the length of the vacuum and boost hoses, tightened everything carefully, sprayed carb cleaner, took out the carbon canister valve and cleaned inside with carb cleaner spray, replaced the gasket, fueled with RON 100 petrol and drove hard for about 20 miles of city traffic and roughly 50 miles of highway.

Conclusion:

- Idle roughness diminished itself to almost nothing;
- Idle still high, about 1000rpm and sometimes jumps slightly above;
- Carbon canister valve does not tick audibly, but it pulsates at idle - it can be felt by touching its top with a finger;
- Manifold vacuum as good as before the repair, in the -0.9bar to -1bar range on the gauge;
- Fuel consumption slightly higher on open road and visibly higher when idling;
- Engine has the best operation under boost I've seen for the last 3 years. No measurable leaks, nothing fluctuates. It raises boost immediately, no hesitation, hits full boost in 3rd gear just by touching the throttle pedal, not even the slight hesitation I had before in 3rd, when it needed a fraction of a second at WOT to hit full boost. Boost gauge needle jumps. Pulls like a train. A TGV train.

I'm going nuts. Or the car does, which for this forum is more or less the same

~Nautilus

 

[Nautilus]

Changed the PCV (in good shape) and crankcase breather tube (so damaged that it crumbled to pieces in my hand).

After a lot of TB adaptations and clearing of fault codes (both by VAG-COM and battery disconnect), it idles erratically, either too high or too low and lumpy, burns a lot of fuel at idle and runs good otherwise. Countless codes appear and disappear on their own, misfire codes, vacuum leak codes, voltage codes, even an "ECU Driver Output IC" code.

TB Position Sensors run like crap (1st sensor in the 14% range at idle, 2nd sensor in the 80% range at idle), manifold vacuum at idle is weak (from -0.2bar to -0.6bar compared to -0.8 to -1.0 before, which translates in too much air going past the throttle plate), and CEL comes on from time to time.

Opened the TB electronics box to check - throttle plate hinge runs from metal stop to metal stop, gears are in good shape, clean inside, stepper motor clean.

It runs very slightly better in wet weather, for unknown reasons. (Even before, when the car was 100% good, the idle was much better in wet weather. As humid air is a better conductor, this can mean poor contact between sensors in dry weather.)

It may be time to spend on a new throttle body, but is it the only culprit here and will the problem clear when the TB is changed?..

~Nautilus

 

[Nautilus]

Problem solved practically by itself, like this:

Symptoms (after countless deletions of faults in VAG-COM and TB adaptation no longer possible): idle 660-720 rpm, very lumpy, light misfires, even more misfires under brake vacuum or A/C compressor on, CEL coming on and staying on, manifold vacuum -0.2 bar at idle compared to -0.8 bar in normal idle, catalyst red-hot, visible in the dark and smelly, idle fuel consumption 1.9-2.1 liters/hour, rather lazy acceleration from a standstill, but engine running well and not misfiring under boost. Ran in this crappy way for 3 days (maybe 60-80 miles), burnt maybe 20 to 30 liters of fuel in this short time (fueled 2 times, each about 15 liters).

Fault codes: misfire code on each cylinder, Random/Multiple Cylinder Misfire (separately), ECU Internal Control Module Output Driver IC (intermittent), voltage fault code, TB Adaptation fault code, O2 sensor no. 1 code combined with a code for the catalyst, and so on (1 page of fault codes, lost count of them all).

Took again the TB down, wiped the 2 throttle sensors in the electronics box with a bit of cleaner sprayed on a tissue and aligned carefully the throttle plate to be exactly 0.3mm from the TB walls on all sides, with a feeler gauge (this was just out of desperation, I didn't think it helped anything).

Deleted again the codes in VAG-COM, performed the TB adaptation again, but this time it adapted perfectly (VAG-COM indicated 8 adaptation attempts before giving an OK indication).

Started the car, got a good idle, a good vacuum (-0.6 to -0.8 bar), idle fuel consumption of 1.0-1.1 liters/hour, no feel of misfires. VAG-COM indicated intermittent misfires on cylinders 1, 2 and 4. Ran for a few miles, misfire count went back to zero.

Left the VAG-COM connected, went for a tough drive on a highway. Boosted up to 1.5 bar, ran up to 200 km/h, the harder that car was driven, the better the indications were: zero misfires, constant 14.0-14.111 volts, good airflow. Ran for about 80 kms on the highway. Running improved itself.

After the highway run, all went back to perfectly normal running: no fault codes, smoothest idle the car ever had in 7 years, idle fuel consumption 0.9 liters/hour, instant throttle response, constant 720 rpm idle, no boost issues, catalyst as hot as it should and no longer smelly, even the slight dipping of the idle rpm when steering which the car previously had disappeared for good.

VAG-COM technician had no explanation for the sudden cure.

My only theory is like this: running with fried coils, freshly-cleaned TB and no electronic adaptation performed, slight vacuum leak due to broken crankcase breather and worn PCV valve together, the ECU could no longer perform any of the usual adjustments which it does when running and went completely nuts. (Like a computer operating system does when it doesn't have the proper drivers installed.) Once the small niggles have been cured (the 4 coils replaced, breather tube replaced, PCV replaced, hose clamps tightened, throttle plate adjusted etc), codes deleted, the TB adaptation could be performed and therefore the ECU could adjust itself to run properly.

~Nautilus